Image reading apparatus

1. An image reading apparatus, comprising: an image reader, operable to read an image corresponding to an original and a back pad, the original being placed on the back pad so that outside of the original contains an area extending in overall width of the back pad, the area being an area in which the original is not disposed; a first data generator, operable to generate first image data based on the image; a second data generator, operable to generate second image data based on a part of the image corresponding to the area, the second image data being a matrix average value of gradation values of predetermined pixels of the part of the image; a first processor, operable to compare the first image data with the second image data pixel by pixel so as to generate first edge information; and a detector, operable to detect an edge of the original based on the first edge information.

2. The image reading apparatus according to claim 1 , further comprising: a second processor, operable to perform image processing to the image so as to clarify contrast difference between the original and the back pad.

3. The image reading apparatus according to claim 1 , further comprising a feeder, operable to feed the original; a mechanical sensor, operable to be brought in contact with the fed original so as to detect the edge of the original; and a second processor, operable to generate second edge information based on the edge detected by the mechanical sensor, wherein the detector detects the edge of the original based on the first and second edge information.

4. The image reading apparatus according to claim 1 , wherein the image corresponds to both sides of the original which are simultaneously read by the image reader, the first edge information includes second edge information associated with one of the both sides of the original and third edge information associated with the other one of the both sides of the original, and the detector detects the edge of the original based on at least one of the first edge information and the second edge information.

5. The image reading apparatus according to claim 1 , further comprising: a second processor, operable to detect a most linear side in the edge of the original including four sides, and to verify the edge of the original detected by the first detector based on the most linear side so as to generate verification information; and a third processor, operable to determine whether the edge of the original is more linear than a predetermined threshold based on the verification information, wherein in a case where the edge of the original is not more linear than the predetermined threshold, image processing is not performed to the image.

6. An image reading apparatus, comprising: an image reader, operable to read an image including a first image corresponding to a first area in which an original is disposed and a second image different from the first image, the second image corresponding to a second area in which the original is not disposed; a generator, operable to generate first image data based on the image and second image data based on the second image, the second image data being a matrix average value of gradation values of predetermined pixels of the second image; and a detector, operable to detect an edge of the original based on the first image data and the second image data.

7. The image reading apparatus according to claim 6 , further comprising a processor, operable to decide whether the first area contains the whole of the original, wherein in a case where the first area does not contain the whole of the original, a user is notified of an error with a message.

8. A method of detecting an edge of an original placed on a back pad, the method comprising: reading an image corresponding to the original and the back pad, the original being placed on the back pad so that outside of the original contains an area extending in overall width of the back pad, the area being an area in which the original is not disposed; generating first image data based on the image; generating second image data based on a part of the image corresponding to the area, the second image data being a matrix average value of gradation values of predetermined pixels of the part of the image; comparing the first image data with the second image data pixel by pixel so as to generate edge information; and detecting the edge of the original based on the edge information.

9. The image reading apparatus according to claim 1 , further comprising a second processor, operable to decide whether the first area contains the whole of the original, wherein in a case where the first area does not contain the whole of the original, a user is notified of an error with a message.